though it leads to no sensible error in practice. The first of the
"park palings" does not stand at A, which is 0°, nor does the
hundredth stand at B, which is 100°, for that would make 101 of them:
but they stand at 0°.5 and 99°.5 respectively. Similarly, all
intermediate _ranks_ stand half a degree short of the _graduation_
bearing the same number. When the class is large, the value of half
a place becomes extremely small, and the rank and graduation may be
treated as identical.

Examples of method of calculating a centesimal position:--

1. A child A is classed after examination as No. 5 in a class of 27
children; what is his centesimal graduation?

_Answer_.--If AB be divided into 27 graduations, his rank of No. 5
will correspond to the graduation 4°.5; therefore if AB be graduated
afresh into 100 graduations, his centesimal grade, x, will be found
by the Rule of Three, thus--

x : 4°.5 :: 100:27; x = 450°/27 = 16°.6.

2. Another child B is classed No. 13 in a class of 25 _Answer_.--If
AB be divided into 25 graduations, the rank of No. 13 will
correspond to graduation 12°.5, whence as before--

x : 12°.5 :: 100 : 25; x = 1250°/25 = 50°; _i.e._ B is the median.

The second method of comparing two statistical groups, to which I
alluded in the last paragraph but one, consists in stating the
centesimal grade in the one group that corresponds with the median